1) Generously grease 4 airtight glass jars of 2 dl capacity and cover the bottom with a baking paper disc. Collect the butter with the sugar and whip them with an electric whisk until the mixture is smooth and fluffy. Then add to the dough, in order: cocoa, 1 egg, half the flour, 1 second egg, the remaining flour, the remaining egg, salt, coarsely chopped chocolate and grated orange zest. Work the mixture with a spatula, combining the next ingredient only when the previous one is well incorporated.

2) Put the marmalade in a small saucepan and let it melt for a few minutes over very low heat. Transfer the chocolate mixture into a pastry bag and squeeze it into the jars, filling them up to halfway; add a spoonful of jam each, cover with the remaining dough and finish with a little jam.

3) Seal the jars hermetically, transfer them to a pot, cover them completely with water and boil (100 °) for 1 hour. Let the cakes cool, remove them from the jars and serve accompanied with a spoonful of sour cream.